Microreactors, which can have improved heat and mass transfer compared to conventional reactors, are a new type of reactor that offer the potential to significantly improve the efficiency of chemical processes. This potential has engendered intense efforts toward developing microreactors, catalysts and micro-processes. A recent review of this technology, containing 236 citations, has been provided by Gavrilidis et al., “Technology And Applications Of Microengineered Reactors,” Trans. IChemE, Vol. 80, Part A, pp. 3-30 (January 2002).
A more conventional approach to reactions in small channels has involved reactions in honeycombs. In U.S. Pat. No. 5,248,251, Dalla Betta et al. described a partial combustion process in which a combustible gas mixture is passed through a monolith that has a graded catalyst in which the catalyst on a leading portion of the support has a higher activity than has the catalyst on a trailing portion of the support.
A recent patent for producing a hydrogen-rich gas describes a catalyst on a honeycomb that has a layer of a partial oxidation catalyst and a layer of a steam reforming catalyst. An embodiment is described in which the catalyst layers are graded such that the partial oxidation catalyst has its maximum thickness near the inlet and diminishes over the length of the catalyst structure to practically zero near the outlet and the steam reforming catalyst has a near zero thickness near the inlet and increases over the length of the catalyst structure to its maximum thickness near the outlet.